The present invention relates to a charging system for electric power tool, a battery pack for electric power tool constituting the charging system, and a battery charger for electric power toll for charging the battery pack.
Conventionally, as a battery pack for electric power tool (hereinafter referred to as a “battery pack”) having a rechargeable battery such as a lithium ion battery and a battery charger for electric power tool (hereinafter referred to as a “battery charger”) for charging the battery pack, those including a microcomputer have been known.
Each of the battery pack and the battery charger has a microcomputer. Therefore, when the battery pack is charged by the battery charger, the charging operation can be meticulously controlled and monitored by the respective microcomputers, whereby proper charging is realized.
Unexamined Japanese Patent Publication No. H09-285026 discloses an example of a method for charging. In the disclosed method, the respective microcomputers mutually perform data communication so as to obtain necessary information thereby realizing more proper charging.
In the above example, for the charging, the microcomputer of the battery charger requests the microcomputer of the battery pack to transmit information indicating a maximum charging voltage and a maximum charging current. In response, the microcomputer of the battery pack transmits the requested information (stored in the battery pack) to the battery charger. After the start of charging, the microcomputer of the battery pack further transmits the present voltage value and the present current value of a battery cell (rechargeable battery) included in the battery pack itself.
The battery charger conducts switching controls between constant-current charge and constant-voltage charge in response to the voltage value of the rechargeable battery during the charging. Specifically, in the constant-current charging, the current is controlled not to exceed the maximum charging current. In the constant-voltage charging, the voltage is controlled not to exceed the maximum charging voltage. As described above, information is transmitted from the battery pack to the battery charger as needed, whereby more appropriate charging can be realized.